Why do people leave their computers on?

Easy to answer...

1. So the user(s) of the computer would not have to reboot the entire hard disk. They simply refresh the sleep mode equipped computer to virtually have an instant start-up.

2. The answer that mostly applies is that people are lazy, and do not care. / or they are downloading something...

- Mike

P.S. (Post Script if you were wondering what that meant ((I know you did :)))) IT IS 3 AM BE HAPPY WITH THE ANSWER, (Reward me with money... seriously)